Draft regulation



Dec. 14, 1937. DA gN 2,102,143

I DRAFT REGULATION I Original Filed March 2, 1933 2 Sheets-Sheet 1 1 .1. 2 V w v T Z h I INVENT m -4- Dec. 14, 193 7.

'G. DALEN DRAFT REGULATION Original Fi led March 2, 1933 2 Sheets-Sheet 2' INVENTO 3% A4" ATTORNEY Patented Dec. 14, 1937 nan-"r amm'rron Gustaf Daln, Lidingo,

Svenska Aktieboiaget Gasaccumulator,

Sweden, aasignor to Stockholm, Sweden, a corporation of Sweden Application Renewed August 14, 1936.

15 Claims.

The present invention relates to draft regulation for combustion apparatus and has particular reference to draft regulation for combustion apparatus of ,the type intended for continuous operation. Still more particularly the invention relates to draft regulation for combustion apparatus intended for continuous operation to heat stoves or the like of heat accumulating character.

In order to obtain an even supply of heat and to obtain high fuel economy numerous types of heating apparatus have been proposed in which heat is absorbed from gases supplied by a continuous combustion process. when heat is developed by continuous combustion the rate of combustion necessary for a given purpose is relatively less than would be the case if combustion were intermittent and heat generated only during the periods when heat is required.

Due to the relatively low rate of combustion in apparatus of the continuous combustion type, the combustion is likely to be interfered with by the unevenness of the draft when draft for combustion is induced by the chimney. This is due to the fact, particularly in the case of heat accumulating apparatuses such as stoves, water heaters and the like, that with continuous combustion at a relatively low rate of velocity of the combustion gases, the gases are cooled to a relatively low temperature before they are delivered to the stack, so that the gases entering the stack are not only comparatively cool but also relatively heavy. If the draft provided by the chimney is even, satisfactory operation will be obtained if the combustion gases are only enough lighter than the surrounding atmospheric air'so that they will flow up the chimney due to the difierence in specific weights of In practice, however, temporary variations in atmospheric pressure or temperature, or both, occur at the'outlet of the chimney, which may and actually do cause variations in the draft produced in the chimney. Under certain circumstances, particularly in windy weather, the outside air pressure may vary to such an extent as to cause back drafts in the chimney. If atmospheric conditions result in an increase in draft the combustion apparatus will operate with excess air, which will decrease the economy of combustion, and if the atmospheric conditions result in a decreasein the draft the combustion apparatus will operate with'incomplete combustion due to lack of suflicient air. Disturbances of the atmospheric air of a more or less temusual natural draft the gases and the outer air.

March 2, 193a, sci-a1 No. 659,301

In Sweden March porary nature may result in still more serio consequences, as for example the back draft of combustion gases into the room in which the combustion apparatus is located. Back draft of combustion gases into the room is always disagreeable, and if it continues for a material length of time may cause the fire to be extinguished and may also involve danger due to the presence of carbon monoxide in the combustion gases forced into the room.

When solid fuel is used for combustion the possibility of permanent extinguishment of the fire due to back drafts is not pronounced, due to the presence of a body of incandescent fuel which will ordinarily cause re-ignition upon resumption of normal draft, but this factor is of con-- siderable importance when gaseous or liquid fuel is employed.

The present invention has for a general object the regulation of the draft from a natural draft source so as to provide a regular and even draft in the combustion chamber of heating apparatus adapted for continuous combustion, regardless of the type of fuel employed.

The nature of the invention, together with the manner in which the above general object and other and more detailed objects are attained may best be understood from a consideration of the following description of suitable apparatus for carrying the invention, into effect, taken in conjunction with the accompanying drawings forming a part of this specification.

In the drawings;

Fig. 1 is a vertical section showing more or less diagrammatically a cook stove of the heat accumulating type provided with draft regulating means embodying the invention; a

Fig. 2 is a section taken on the line 2-2 of Fig. 1;

Fig. 3 is a view showing a modified form of a part of the draft regulating means; and,

Fig. 4 is a more or less diagrammatic vertical section through another heat accumulating stove having a different type of fuel burning apparatus than that shown in Fig. 1 and having draft regulating means embodying the invention.

Turning now more particularly to Fig. 1, the heating apparatus shown thereinis a heat accumulating cook stove of the general type disclosed in United States Patent No. 1,559,162 granted to me October 27, 1925 and in which continuous combustion is employed to heat a heat accumulating mass within the stove, which mass stores and delivers the heat required for cooking purposes.

The stove comprises a mass of heat accumulating metal l0 surrounded by thick insulation ll enclosed in a light outer casing l2, preferably of metal. The mass l0 provides a hot plate or cooking surface l3 which, when not in use, is advantageously covered by a heavy hinged cover ll of suitable insulating material. In the embodiment illustrated, the mass of metal ID has an interior flue for combustion gases comprising a vertically extending portion l5 and a horizontally extending portion l6. Combustion gases are carried from the portion l6 by a conduit l1 passing through the insulation and constituting a continuation of the flue. At the bottom of the portion l5 of the flue there is located a burner It for combustion of fuel supplied to the burner in the form of gas. The stove illustrated is adapted to be operated by liquid fuel which in the embodiment shown is supplied through an oriflce I 9 in a drip member 20 to a vaporizing chamber 2|. The bottom of chamber 2| is formed by a hot vaporizing plate 22 in direct heat conducting relation with the mass ill, from which it derives the heat necessary to vaporize the fuel dropping from the orifice IS. The vaporized fuel passes from chamber 2| to the chamber 23, to which air for combustion is admitted, this chamber constituting the mixing or carbureting chamber. A baille 24 in chamber 23 assists in mixing the air and vaporized fuel and the resulting combustible mixture passes to the burner l6, which may be of any suitable type. Adjacent to the stove and outside of the insulation a casing 25, preferably of metal, forms a chamber 26, the upper portion of which is connected to the chimney 21 by a connection 28, and the lower portion of which is placed in communication with the atmosphere of the room in which the stove is located by a connection 29. Conduit l1, forming a portion of the combustion gas flue within the stove, communicates with the upper portion of chamber 26. Air for combustion is delivered to the chamber 23 from the lower portion of chamber 26 by way of conduit 30.

As will be evident from Fig. 2, chamber 26 is of relatively large cross-sectional area as compared with the cross-sectional area of the flue connecting the combustion space with the upper portion of the chamber, and the resistance to flow of air through the chamber is relatively very slight as compared with the resistance to flow of combustion gases through the burner and the flue.

The device operates as follows. Fuel is vaporlzed in the chamber 2| and the fuel vapor mixes with combustion air in chamber 22 and is burned at burner l6. Thecombustion gases rise through the flue portion I5 and pass by way of the flue portions l6 and I1 and the upper portion of chamber 26 and connection 26 to the chimney 21, In their passage through flue portions l5 and I6 the gases are cooled to a relatively low tempera the heat from the gases being absorbed in the heat accumulating mass l6, which stores the heat so as to have it available for use at the hot plate l3, and which also provides a source of heat by conduction for maintraining the vaporizing surface 22 at high temperature The contents of-chamber 26 consist mainly of cold or relatively slightly heated fresh air so that the contents of the chamber are of relatively high specific weight. On the other hand, the column of combustion gases in the flue space is hot and of relatively low specific weight. If the effect of the draft from the chimney is neglected it will be evident that due to the difference in specific weights of the columns in chamber 26 and in the flue space, there would be upward flow of combustion gases in the flue space and downward flow in the chamber 26. The gases in the chimney are, however, of lower specific weight than that of the outside air and therefore rise and produce an upward draft which is applied to the upper portion of the chamber 26. The column of air in chamber 26 and also the gases in the flue space are subjected to this draft which may be said to be divided at the upper portion of the chamber. Due, however, to the very small resistance to flow through the chamber 26 compared with the resistance to flow through the flue space, the major portion of the draft from chimney 21 will be through chamber 26. The total draft of gases to the chimney will consist of a relatively small percentage of combustion gases from the flue space and a relatively large percentage of air through chamber 26, and with this arrangement it will be evident that fluctuations in the draft produced by the chimney will be absorbed by variations in flow of air in chamber 26 rather than by variations in the rate of flow of combustion gases in the flue space. This obviously will result in a relatively even 'draft through the combustion and flue space in spite of fluctuations in the value of the draft produced by the chimney.

I'he upper portion of chamber 26 contains hot combustion gases and the lower portion contains cool or slightly heated fresh air. Except fora small ame of diffusion between the combustion gases and the air, these different gases will be contiguous along a horizontal or substantially horizontal layer. In the arrangement shown in the drawings, in which the flue conduit l1 opens into the upper portion of chamber.26 at a level somewhat below the connection 26, this layer will ordinarily be located somewhere between the lower edge of conduit l1 and the upper edge of connection 26. Upon an increase in the draft of the chimney to a value above normal, this layer will be raised above the intermediate position indicated by dotted line 3 I to a position such, for example, as indicated at 32, so that flue gases will pass to the chimney from the conduit I I and more air will pass to the chimney from chamber 26. Upon a decrease in the draft to a value bethus forced out of chamber 26 and may flow partly into the room surrounding the chamber and partly through the connection 36 to the combustion space. In case of actual back draft through the chimney, chamber 26 will fill comparatively rapidly with combustion gases, but the chamber should be made sufllciently large that the back drafts ordinarily encountered will not cause the combustion gases to ill] the chamber to a level as low as that indicated at 26. In case of a back draft of exceptional. duration, or in case the chimney should become obstructed, so that the level of the combustion gases inchamber 26 falls below 7 thatindicated at 34, inert combustion gases will .flow to the combustion space and combustion will cease. It will be observed that if the conduit 30 did not connect chamber 26 with chamber 28 but instead connected the latter chamber with the outside atmosphere, combustion would not cease even in thecase of continuous back draft or obstruction in the chimney. On the other hand, if this change were made, combustion gases, in the event of continuous back draft, would enter the room in which the stove is located and would involve danger due to carbon monoxide gas, because even with such back draft combustion would continue and there would be flow upwardly through the combustion flue of hot combustion gases which would in turn be carried down the check draft flue by the back draft. If the room were small, the entry of combustion gases would serve to decrease the oxygen content of the air in the room and aggravate the production of carbon monoxide because of the relatively low oxygen content of the air continuing to be burned in the combustion space. By connecting the conduit 30 to chamber 26, this effect is avoided due to the fact that when a source of prolonged back draft occurs, combustion gases suflicient to extinguish the fire will flow through conduit 30 before a harmful amount of combustion gases can have entered the room, and combustion will cease until normal draft is again established. Upon the resumption of normal draft, or scient draft to lift the level of combustion gases above that indicated at it, fresh air will flow to the combustion space, and in case solid fuel is employed, combustion will recommence due to the temperature of the body of incandescent fuel. Where oil or gaseous fuel is employed, combustion will ordinarily recommence in apparatuses of the heat accumulating type shown in the drawings, since the amount of heat storediat high temperature will be sufficient to produce ignition upon resumption of the normal supply of air for combustion.

From the foregoing it will be evident that the chamber 26 provides what may be termed a cushion comprising a relatively large body of cool air in a chamber, the internal aerodynamic resistance of which is so small as compared with the aerodynamic resistance of the burner and flue, that draft fluctuations are absorbed by this cushion.

.The chamber 26 provides a practical advantage in that it aifords a location for the reservoir or reservoirs for oil in the case of on burning combustion apparatus. A suitable location for such reservoirs is always more or less a dimcult matter because of the difliculty of eliminating diffusion into the room in which the apparatus is located of the objectionable odors from the oil.

With the above described apparatus, the oil reservoir, indicated at 35 may conveniently be placed within the chamber 26, with an external filling opening (not shown) and when placed in this manner any objectionable odors which may arise will be carried into the chimney. Fuel from the reservoir 35 is supplied to the drip member 20 by means of a suitable connection 36.

Itis important that the temperature of the walls of chamber 26 does not vary materially,

to the burner through the connection so might be mixed with inert combustion gases, resulting in incomplete combustion at the burner. Inner circulation within chamber 26 is prevented in the first place by making the chamber, as will be evident from Figs. 1 and 2, with a horizontal cross-sectional area which is small as compared with the vertical cross-sectional area. Further, in accordance with one feature of the invention, the upper part of chamber 26, which usually contains combustion gases, is made with a relatively small. horizontal cross-sectional area while the lower part of the chamber which ordinarily contains fresh air is of much greater cross-sectional area. With this arrangement, resistance to flow of gases in the chamber in internal circuits is increased without there being an appreciable increase in the resistance to flow of gases in a direct line longitudinally of the chamber. It is in order to diminish the risk of internal circulation within the chamber that the walls thereof are made, as previously noted, of metal or other material having good heat conductivity characteristics.

Further, as shown in Fig. 3, internal flanges such as those indicated at 311, or like means, may beiixed to the walls of the chamber to provide additionalresistance to local flow of gas in the chamber along the walls thereof.

Turning now more particularly to Fig. 4, another embodiment of the invention is shown in more or less diagrammatic form. In this arrangement, combustion is provided for by a gas burner of a kind different from that shown in a Fig. l. The burner comprises a base til of generally cup-shaped form supporting two concentric perforated pipes M and t2. An outer casing it supports a pipe it concentric with and spaced from the pipe d2. Pims M and M are closed at their upper ends while the annular space t5 between pipes ti and 42 is in communicationwith the vertically extending flue space l5a. Gaseous fuel is supplied to the base Mi of the burner through a suitable connection (not shown in the drawings) and air for combustion is supplied to the space it within pipe 4i through the connection Mia and to the space 41 between pipes at and it through the connection 30b. The combustion air, passing through the perforations in pipes M and 42 mingles with the gaseous fuel to form a combustible mixture, combustion taking place in the space it. Combustion gases rise through the flue portion iba to the flue passage IGa in the heat accumulating mass Ilia which provides the hot I plates or cooking surfaces l3a and 13b and which is in heat conducting relation with the Walls of the cooking and warming ovens indicated respectively at 48 and 49.

From the flue space l6a the combustion gases pass to the chimney (not shown) through the outlet connection 28a. A fresh air chamber 26a, consisting of a verticaJy extending portion and a horizontally extending portion communicates at its upper end with the connection 28a and at its lower end communicates with the atmosphere through the opening 29a. Connections 30a and 30b for supplying combustion air to the burner communicate with the lower portion of the chamber 26a.

It will be evident that this embodiment of the invention operates in a manner similar to that previously described in connection with Fig. 1.

' Chamber 26a has considerably less aerodynamic resistance than that of the burner and combustion gas flue and provides a cushion of air which absorbs fluctuations in the value of the draft induced by the chimney at the connection 28a.

From the foregoing description it will be apparent that the invention may be embodied in many diiierent forms and arrangements of apparatus and it is to be understood that the invention is not limited to the forms of apparatus hereinbefore described by way of illustration but is to be considered as including all such arrangements as may fall within the terms of the appended claims, when construed as broadly as is consistent with the state of the prior art.

What I claim is:

1. Fuel burning apparatus adapted to be operated with a natural draft chimney comprising means forming a chamber for air in communication with the chimney, a continuously open inlet for supplying air to the lower part of said chamber, means forming a combustion space and a flue for combustion gases connecting said space with the chimney, means for supplying fuel to said space and means for supplying substantially allof the combustion air required for burning the fuel in said space under all conditions of normal operation of the apparatus comprising a continuously'open connection connecting said combustion space with said chamber at a place remote from the place of communication with the chimney and between the last mentioned place and said inlet, said chamber and said connection providing a continuously open path arranged to cause flue gases to flow from the chimney to said combustion space prior to flow thereof to said inlet upon continued back draft, and said chamber having such length and cross sectional area and configuration and being so arranged as to provide less resistance to flow of air therethrough than the resistance to flow of air and combustion gases through said connection, said combustion space and said flue;

2. Fuel burning apparatus adapted to be operated with a natural draft chimney comprising means forming a chamber for air in communication with the chimney, an open inlet having substantially less cross sectional area than the cross sectional area of said chamber for supplying air to the lower part of said chamber, means forming a combustion space and a flue for combustion gases connecting said space to the chimney, means for supplying fuel to said space and means for supplying substantially all of the combustion air required for burning the fuel in said space comprising an open connection connecting the combustion space with said chamber at a place remote from the place of communication with the chimney and between the last mentioned place and said inlet, said chamber providing a continuously open connection between the chimney and the connection leading to the combustion space, and said chamber having such length and cross sectional area and configuration and being so arranged as to provide less resistance to flow of air therethrough than the resistance to fiow of air and combustion gases through said connection, said combustion space and said flue.

3. Fuel burning apparatus adapted to be operated with a natural draft chimney comprising means forming an upwardly extending chamber for air, the upper portion of said chamber being in communication with the chimney, a continuously open inlet having a cross sectional area very much smaller than the horizontal cross sectional area of said chamber for supplying air to the lower part of said chamber, means forming a combustion space and an upwardly extending flue for combustion gases connecting said space with the chimney, means for supplying substantially all of the combustion air required for burning the.

fuel in said space comprising a continuously open connection connecting the combustion space and a place in the lower portion of said chamber be-- tween the place of communication with the chimney and said inlet, said chamber providing a continuously open connection between the chimney and the connection leading to the combustion space and said chamber having such length and cross sectional area and configuration and being so arranged as to provide less resistance to flow of air therethrough than the resistance to flow of air and combustion gases through said connection, said combustion space and said flue.

4. Fuel burning apparatus adapted to be operated with a natural draft chimney comprising means forming an upwardly extending chamber for air, the upper portion of said chamber being in communication with the chimney, a continuously open inlet having very much smaller cross sectional area than the horizontal cross sectional area of said chamber for supplying air to the lower part of said chamber, means forming a combustion space and a flue for combustion gases connecting said space with the chimney, means for supplying fuel to said space and means for supplying substantially all of the combustion air required for burning the fuel in said space comprising a continuously open connection connecting the combustion space with the lower portion of said chamber at a place above the level of said inlet and between said inlet and the place of communication of the chamber with the chimney, said chamber providing a continuously open connection between the chimney and the connection leading to the combustion space and said chamber having such length and cross sectional area and configuration and being so arranged as to provide less resistance to flow of air therethrough than the resistance to flow of air and combustion gases through said connection, said combustion space and-said flue.

5. Fuel burning apparatus adapted to be operated with a natural draft chimney comprising means forming a'chamber for air in communication with the chimney, a continuously open inlet for supplying air to the lower part of said chamber, said inlet having a cross sectional area substantially less than that of said chamber, means forming a combustion space and a fiue for combustion gases connecting said space with the chimney, means for supplying fuel to said space, means for supplying substantially all of the combustion air required for burning the fuel in said space under all conditions of normal operation of the apparatus comprising a continuously open connection connecting said combustion space with said chamber at a place remote from the place of communication with the chimney and between the last mentioned place and said inlet, said chamber providing a continuously open connection between the chimney and the connection leading to the combustion space, and said chamber having such length and cross sectional area and configuration and being so arranged as to provide less resistance to flow '01 air therethrough than the resistance to flow or air and combustion gases through said connection, said combustion space and said flue. and means within said chamber for minimizing local circulation 01' air ad Jacent to the walls of the chamber.

. 6. Fuel burning apparatus adapted to be operated with a natural draft chimneycomprlsing bustible gaseous fuel to said space comprising a liquid fuel vaporizer, a channel connecting said vaporizer and said space and a continuously open connection connecting said channel with a place in the lower portion of said chamber between the place of communication with the chimney and said inlet, said chamber and said connection providing a continuously open path arranged to cause flue gases to flow from the chimney to said combustion space prior to flow thereof to said inlet upon continued back draft, and said chamber having such length and cross sectional area and configuration and being 50' arranged as to provide less resistance to flow of air therethrough than the resistance to flow of air and combustion gases through said connection, said combustion space and said flue.

'7. Heating apparatus of the type adapted to be heated by continuous combustion with draft induced by a natural draft chimney comprising heat insulated means within the apparatus forming a combustion space and a flue for combustion gases connecting said space with the chimney and including a part in intimate heat exchange relation with the gases passing through said flue, said part having a heat delivering surface and being adapted to be maintained continuously at working temperature by transfer of heat thereto from the combustion gases flowing continuously in contact therewith at relatively slow rate, means forming a chamber for air in communication with the chimney comprising walls in direct heat conducting relation with the atmosphere whereby to keep the temperature of said chamber relatively constant, a continuously open inlet having a cross sectional area many times less than the cross sectional area of said chamber for supplying air to the lower part of the chamber, means for supplying fuel to said space and means for supplying substantially all of the combustion air required for burning the fuel in said space comprising a continuously open connection connecting said space and a place in the lower portion of said chamber between the place of communication with the chimney and said inlet, said chamber having such length and cross sectional area and configuration and being so arranged as to provide less resistance to flow of air therethrough than the resistance to flow of air and combustion gases through said connection, said combustion space and said flue.

8. Heating apparatus of the type adapted to be heated by continuous combustion with draft induced by a natural draft chimney comprising heat insulated means within the apparatus forming a combustion space and an upwardly extending flue for combustion gases connecting said space with thechimney and including a part in intimate heat exchange relationwith the gases passing through said flue, said part having a heat delivering surface and being adapted to be maintained continuously at working temperature by the transfer of heat thereto from the combustion gases flowing continuously in contact therewith,

said flue and said part having suflicient surface area in contact with said gases to reduce the rem, perature thereof to a relatively low value before they reach the outlet of the flue, means forming an upwardly extending chamber for air in direct heat conducting relation with the atmosphere,"

the upper portion of said chamber being in communication with the chimney, a continuously open inlet having a cross sectional area many times less than the horizontal cross sectional area of the chamber for supplying air to the lower portion of the chamber, means for supplying air to said combustion space and means for supplying substantially all of the air required to burn the fuel in said space comprising a continuously open and unregulated connection connecting said space and a place in the lower portion of said chamber above the level of said inlet and between said inlet and the place of communication of the chamber with the chimney, said chamber having such length and cross sectional area and configuration and being so arranged as to provide less resistance to flow of air therethrough than the resistance to flow of air and combustion gases through said connection, said combustion space and said flue.

9. Ina stove adapted to be operated with a natural draft chimney, a burner structure providing a combustion space and including a heavy metal heat-storing mass closely adjacent to and in intimate heat conducting relation with said space, said burner structure being located within the stove and substantially entirely enclosed with heat insulating material whereby to cause said heat-storing mass to be maintained at high temperature during normal operation of the stove, means providing a flue within the stove for connecting said space with said chimney at a level above the combustion space, means forming a chamber for air in communication with said chimney, a continuously open inlet for supplying air to the lower part of said chamber, and means forming a continuously openconnection for supplying substantially all of the air required for combustion to said space from a zone in said chamber below and remote from the place of communication between the chamber and the chimney, said chamber having such length and cross-sectional area and configuration and being so arranged as to provide less resistance to flow of air therethrough than the resistance to flow of air and combustion gases through said connection, said combustion space and said, flue, said connection communicating with said chamber at a level above that of said inlet at a place between said inlet and the place of communication of the chamber with the chimney and said chamber and said connection providing a continuously open path arranged for flow of flue gases from the chimney to the combustion space prior to the flow thereof to said inlet upon continued back draft.

10. In a stove adapted to be operated with a natural draft chimney, a burner structure providing a combustion space and including a heavy metal heat-storing mass closely adjacent to and in intimate heat conducting relation with said space, said burner structure being located within the stove and substantially entirely enclosed with heat insulating material whereby to cause said heat-storing mass to be maintained at high temperature during normal operation of the stove, means providing a flue within the stove for connecting said space with said chimney at a level immediately above the combustion space, means forming a chamber for air in communication with said chimney, "inlet means to supply alr to the lower part of said chamber from the ambient atmosphere, and means providing a continuously open connection for supplying substantially all of the air-for combustion to said space, said connection having an inlet in communication with a zone in said chamber remote from and substantially below the place of communication of the chamber with the chimney, said inlet being located between the said place of communication of the chamber with the chimney and said inlet for air in the path of flow of gaseous fluid through the chamber, said chamber and said connection providing a continuously open path arranged for flow of fine gases from the chimney to the combustion space prior to the flow thereof tosaid inlet upon continued back draft and said chamber having such length and cross-sectional area and configuration and being so arranged as to provide less resistance to fiow of air therethrough than the resistance to flow of air and combustion gases through said connection, said combustion space and said flue.

11. -Heating apparatus of the kind having a combustion space and adapted to be heated by continuous combustion with natural draft, including means forming a confined air space for confining an air cushion consisting of a relatively large body of cool air, connections placing the upper part of said space in communication with the draft producing flue of the apparatus and the lower part of said space with the ambient atmosphere for causing said cushion of air to be drawn by said draft into said confined air space, a connection providing for flow of combustion gases from said combustion space to the upper portion of said confined air space and means providing a passage for continuously supplying to said combustion space substantially all of the air required for combustion, the inlet of said passage opening into said confined air space and being located so that the air entering said passage is supplied thereto from said cushion of confined air.

12. Heating apparatus of the kind having a combustion space and adapted to be heated by .continuous combustion with natural draft, in-

cluding means forming a confined air space for confining an air cushion consisting of a relatively large body of cool air, an atmospheric air inlet opening into the lower portion of said confined air space, a connection opening into the upper portion of said confined air space and in communication with the draft producing flue of the apparatus for causing said cushion of air to be drawn by said draft into said confined air space, a connection from said combustion space opening into the upper portion of said confined air space, and means providing a passage for continuously supplying to said combustion space substantially all of the air requiredi'or combustion, the inlet of said passage opening into the lower portion of said confined air space but at a level above that. of the atmospheric air inlet whereby to cause the air for combustion to be drawn from the lower portion of the body of air forming said air cushion.

13. Fuel burning apparatus adapted to be operated with a natural draft chimney comprising a combustion space and a flue for combustion gases, means for supplying fuel to said space, means for supplying air to said space for combustion and to said chimney including a channel leading to the chimney and a continuously open connection connecting said channel with said space, said channel being in communication with said flue and in heat insulated relation with said combustion space, and said channel having such length and cross sectional area and configuration and being so arranged as to provide less resistance to flow of air therethrough than the resistance to flow of air andcombustion gases through said connection, said combustion space and said flue, and a restriction located in the path for flow of air from the ambient atmosphere through said channel to said chimney, said restriction being located outside the portion of said channel situated between the place of communication of said channel with said flue and the place of communication of said channel with said connection.

14. Fuel burning apparatus adapted to be operated with a natural draft chimney including means forming a combustion space, means forming a channel for air, connections providing communication between the upper portion of said channel and said chimney and the lower portion of said channel and the atmosphere, whereby to cause draft from the chimney to draw air through said channel, a connection between said channel and said combustion space for supplying combustion air to said space and means for supplying fuel to said combustion space including a reservoir for liquid fuel located in said channel.

15. Fuel burning apparatus adapted to be operated with a natural draft chimney including means forming a combustion space, means forming a channel for air, connections providing communication between the upper portion of said channel and said chimney and the lower portion of said channel and the atmosphere, whereby to cause draft from the chimney to draw air through said channel, a connection between said channel and said combustion space for supplying combustion air to said space, means for supplying fuel to said combustion space including a reservoir for liquid fuel located in said channel, and means for insulating said channel from heat generated in said combustion space.

GUS'I'AF DALE'N. 

